Analysis And Experimental Research On Bimetal Conductive System Of Thermal Overload Relay

The thermal relay,as the auxiliary accessories of the contactor,is mainly used for the protection of the overload and lack of phase on the motor.With the development of modern industry,industrial control electrical appliances are also developing towards miniaturization.However,too small volume will affect the functional requirements of the internal structure of the product.For example,bimetal conductive system of thermal overload relay of shown in this paper has the following features: the decrease of the product volume(based on the length and height of the product little changed)brings width decrease,will lead to lack of bimetal motion space.The width of thermal overload relay determines the way to install and numbers of thermal overload relay in the low voltage switchgear.Therefore,the size of the low voltage switchgear(the number of installed)and motion space of thermal overload relay has become the opposite relationship.In this paper,the contradiction is solved by combining the theory with practice and using the simulation software to modify the model and verify the actual functionality.The main contents including the analysis and verification are carried out around the following aspects:(1)The change of width has a great influence on the assignment of configuration of the conductive system.Therefore,based on the study of TRIZ theory,four conceptual design schemes of horizontal layout,longitudinal layout,cross layout and electronic layout are obtained.Using the DFSS conceptual choice,the longitudinal layout scheme was proposed.Due to low cost,simple structure,multiple functions for bimetal-thermal overload relay,it was the most widely used in the market at present.The key component is the thermal bimetal.The generated heat results in shape changed on the thermal bimetal after the current flows,which leads to the deformation that bring the displacement and force.Therefore,it realizes the opening and closing of the thermal overload relay.The temperature rise model of thermal bimetal conduction system is established for thermal overload relay through the research on the principle of its working mechanism.(2)Using ANSYS software to simulate and adjust the temperature rise of the threephase conductive system for longitudinal layout design programs and by changing the shape of the outlet terminal and the internal structure to change the air flow in order to achieve the consistency of the temperature rise of three-phase conductive system.Prototypes were produced for actual measurement.After the simulation results were close to the actual measurement results,the temperature rise simulation of the horizontal and vertical installations was further compared and the displacement test of the double gold conductive system was verified.Finally,the feasibility and reliability of the design scheme is verified through the overload protection performance test complied with GB standard.(3)After running for a period of time,the normal distribution data from the test data of the 1.05 In and 1.2In overload trip times for the 84 pcs products was summarized and analyzed by Minitab software.The Johnson data was used for the data that did not meet the normal distribution.The formula is used for data conversion.Normal analysis of the converted data is used to obtain the overload test time of 15 min as the samples' tested time complying with GB standard,and its process capability is analyzed.In the case of guaranteeing product quality,the original 2 hours were shortened to only 15 minutes,further improving the test efficiency and satisfying the need for mass production and testing of products.According to the research results,under the condition of ensuring the original length and thickness of the product,a thermal overload relay with a width of only 27 mm was obtained,and the width was reduced by 40% compared to the conventional 45 mm wide product.The thermal overload protection relay product with the construction of bimetal conductive system of longitudinal layout is adopted,and the feasibility of product mass production is realized.It provides reference for the design,simulation and production of similar products.The successful development of new products will benefit low-voltage electrical equipment manufacturers and design engineers to reduce size of the low voltage switchgear(without affecting the product's internal operating space)and reduce influence of the environment.